In underground formations penetrated by drilled boreholes wherein the formations contain loose sands and soft sandstone strata, a constant problem in well flow through the borehole involves the migration of the loose sands and degraded sandstone into the well bore due to destruction of the formation caused by the pressure and flow of the fluids therethrough.
While numerous techniques have been used to prevent this migration of fine particles which clog the production system and seriously erode the tools in the string, two basic techniques have evolved. The first is basically a chemical treatment involving injection of a fluid into the formation and reacting the fluid chemically or with heat to set up a permeable gel or solid to retain the sand while allowing fluid flow therethrough. This method suffers from a lack of homogeneity caused by voids in the gel due to incomplete saturation of the initial fluid and the setting fluid.
The second technique involves a physical technique of placing a graded aggregate in the borehole to form a porous screen between the production string and the formation wall. This technique is commonly referred to as gravel packing and generally involves the placement of finely graded aggregate such as ottawa sand, walnut shells, glass beads, etc., through a crossover tool or by a washing-in tool.
These tools suffer from the disadvantages of complexity, contamination of pumps, and moving parts with the aggregate, and a lengthy multi-step process of gravel placement. For instance, when the liner is washed into place, at least two runs of the tool string into the well bore are required for each aggregate pack.
Also the prior devices result in a great infusion of circulating fluid into the formation to place the aggregate. This is undesirable in that it interferes with the normal flow of formation fluids to the well bore. Furthermore, the prior devices do not offer the degree of control which is desirable when zones of high-pressure are being treated.